Using HTTP you can't reliably get listings of all files in a directory. Are you talking about a listing like "ls" would give you? You can't get that over HTTP, unless you're implementing both ends of the request--in other words, unless you've implemented some server-side script to print out a directory listing for a given directory.

In any case, look into LWP for making HTTP requests--you can use this to fetch the files, once you know what files you'd like to fetch.